• Nuclear Engineering and Technology
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• 제55권5호
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• pp.1911-1923
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• 2023

The nuclear safety assessment involving large transient simulations is forcing the community to develop methods for coupling thermal-hydraulics and neutronic codes and three-dimensional (3D) Computational Fluid Dynamics (CFD) codes. In this paper a set of dynamic boundary conditions are implemented in OpenFOAM^Ⓡ in order to apply zero-dimensional (0D) approaches coupling with 3D thermal-hydraulic simulation in a single framework. This boundary conditions are applied to model pipelines, tanks, pumps, and heat exchangers. On a first stage, four tests are perform in order to assess the implementations. The results are compared with experimental data, full 3D CFD, and system code simulations, finding a general good agreement. The semi-implicit implementation nature of these boundary conditions has shown robustness and accuracy for large time steps. Finally, an application case, consisting of a simplified open pool with a cooling external circuit is solved to remark the capability of the tool to simulate thermal hydraulic systems commonly found in nuclear installations.

• Structural Engineering and Mechanics
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• 제88권3호
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• pp.263-271
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• 2023

Base isolation is a widely used technique for the seismic control of structures as it reduces the structural seismic demand. However, displacement of the isolation layer is not economically feasible in congested urban areas. To resolve the issue, an innovative system is proposed here to isolate both horizontally at the base and vertically in the upper portion of the structure. A simplified linear three degree-of-freedom (3DOF) model of the system that considers the mass and stiffness ratios of the substructure has been introduced and analyzed in MATLAB by spectrum analysis. The 3DOF model results revealed that, when the period of the soft substructure reaches 2.5 times that of the stiff substructure, the isolation and the lower substructure responses decrease by 65% and 51%, respectively. Time-history analysis of a MDOF system at three frequency ratios under a wide range of ground motions indicated that, at the expense of accepting a certain large drift by the soft substructure in the upper portion of the structure, base isolation displacement can be decreased by 10%.

• 시스템엔지니어링학술지
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• 제19권2호
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• pp.46-58
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• 2023

Deterministic safety analysis is a crucial part of safety assessment, particularly when it comes to demonstrating the safety of nuclear power plant designs. The traditional approach to deterministic safety analysis models is to model the nuclear core using point kinetics. However, this simplified approach does not fully reflect the real core behavior with proper moderator and fuel reactivity feedbacks during the transient. The use of Multi-Physics approach allows more precise simulation reflecting the inherent three-dimensionality (3D) of the problem by representing the detailed 3D core, with instantaneous updates of feedback mechanisms due to changes of important reactivity parameters like fuel temperature coefficient (FTC) and moderator temperature coefficient (MTC). This paper addresses a CEA ejection accident at hot full power (HFP), in which the underlying strong and un-symmetric feedback between thermal-hydraulics and reactor kinetics exist. For this purpose, a multi-physics analysis tool has been selected with the nodal kinetics code, 3DKIN, implicitly coupled to the thermal-hydraulic code, RELAP5, for real-time communication and data exchange. This coupled approach enables high fidelity three-dimensional simulation and is therefore especially relevant to reactivity initiated accident (RIA) scenarios and power distribution anomalies with strong feedback mechanisms and/or un-symmetrical characteristics as in the CEA ejection accident. The Systems Engineering approach is employed to provide guidance in developing the work in a systematic and efficient fashion.

• 대한핵의학회지
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• 제30권3호
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• pp.299-314
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• 1996

The purpose of the present study was to validate the use of tissue radioactivity ratios instead of regional metabolic rates for the assessment of regional metabolic changes in Alzheimer's disease(AD) with [$^{18}F$]FDG PET and to examine the correlation of ratio indices with the severity of cognitive impairment in AD. Thirty-seven AD Patients(age $68{\pm}9 yrs$, $mean{\pm}s.d.$; 36 probable and 1 definite AD), 28 patients with dementia of non-Alzheimer type(age $66{\pm}7 yrs$), and 17 healthy controls(age $66{\pm}4 yrs$) underwent [$^{18}F$]FDG PET imaging. Two simplified radioactivity ratio indices were calculated from 37-66 min image: region-to-cerebellar radioactivity ratio(RCR) and a composite radioactivity ratio(a ratio of radioactivity in the most typically affected regions over the least typically affected regions: CRR). Local cerebral metabolic rate for glucose(LCMRglu) was also measured using a three-compartment, five-parameter tracer kinetic model. The ratio indices were significantly lower in AD patients than in controls(RCR in temporoparietal cortex, $0.949{\pm}0.136$ vs. $1.238{\pm}0.129$, p=0.0004; RCR in frontal cortex, $1.027{\pm}0.128$ vs. $1.361{\pm}0.151$, p<0.0001; CRR, $0.886{\pm}0.096$ vs. $1.032{\pm}0.042$. p=0.0024). On the RCR analysis, 86% of AD patients showed a pattern of bilateral temporoparietal hypometabolism with or without frontal involvement; hypometabolism was unilateral in 11% of the patients. When bilateral temporoparietal hypometabolism was considered to be suggestive of AD, the sensitivity and specificity of the RCR analysis for the differential diagnosis of AD were 86% and 73%, respectively. The RCR was correlated significantly with the macroparameter K [$K_1k_3/(k_2+k_3)$] (r=0.775, p<0.0001) and LCMRglu(r=0.633, p=0.0002) measured using the kinetic model. In patients with AD, both average RCR of cortical association areas and CRR were correlated with Mini-Mental Status Examination(r=0.565, p=0.0145; r=0.642, p=0.0031, respectively), Clinical Dementia Rating(r=-0.576, p=0.0124; r=-0.591, p=0.0077), and total score of Mattis Dementia Rating Scale (r=0.574, p=0.0648; r=0.737, p=0.0096). There were also significant correlations between memory and language impairments and corresponding regional RCRs. The results suggest that the [$^{18}F$]FDG PET ratio indices, RCR and CRR, reflect global and regional metabolic rates and correlate with the severity of cognitive impairment in AD. The simplified ratio analysis may be clinically useful for the differential diagnosis and serial monitoring of the disease.

• 한국환경복원기술학회지
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• 제17권4호
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• pp.57-67
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• 2014

The vigor condition of trees is an important indicator for the management of urban forested area. But difficulties in how to assess the tree vigor condition still remain. Previous efforts were limited in the 1) measurement of single indicator rather than using multiple indices, 2) purpose-oriented measurement such as for air-pollution effect or specific pathological symptom, and 3) ordinal-scale evaluations by field crews 4) despite human errors based on his/her experiences or prior knowledge. Therefore, this study attempted to develop a quantitative and objective methodology for assessing tree vigor condition, by measuring multiple modules and building the profile inventory. Furthermore, the possibility and limitations were discussed in terms of schematic frames describing tree vigor condition. The vigor condition of 56 flowering cherry plants in urban park were assessed by in-situ measurements of following eight items; growth of crown(Gc), growth of shoots, individual tree volume(Vol), plant area index, woody area index, leaf area index, leaf chlorophyll content(Lc) and leaf water content(Lw). For validation, these measurements were compared with the ranks of holistic tree vigor condition, which were visually assessed using a 4-point grading scale based on the expert's knowledge. As a result, the measures of each evaluation item successfully highlighted a variety of aspects in tree vigor condition, including the states of both photosynthetic and non-photosynthetic parts. The variation in the results depending on evaluated parts was shown within an individual tree, even though the broad agreement among the results was found. The result of correlation analysis between the tested measurements and 4-point visual assessment, demonstrated that the state of water-stressed foliage of the season (Lw) or the development of plant materials since sapling phase (Vol) could be better viewed from the outer appearance of trees than other symptoms. But only based on the visual assessment, it may be difficult to detect the quality of photosynthesis (Lc) or the recent trend in growth of trees (Gc). To make this methodology simplified for the broad-scale application, the tested eight measurements could be integrated into two components by principal component analysis, which was labelled with 'the amount of plant materials' and 'vigor trend', respectively. In addition, the use of these quantitative and multi-scale indicators underlies the importance of assessing various aspects of tree vigor condition, taking into account the response(s) on different time and spatial scale of pressure(s) shown in each evaluated module. Future study should be advanced for various species at diverse developing stages and environment, and the application to wide areas at a periodic manner.

• 한국산학기술학회논문지
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• 제18권4호
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• pp.599-607
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• 2017

본 논문은 2015년 화학물질관리법 시행에 따라 일정 수량 이상 화학물질을 취급함으로써 장외영향평가서와 위해관리계획서를 제출할 의무가 있는 영세 및 중소기업들을 대상으로 행정 경제적인 부담을 줄이고자 위험성 평가에 대한 실질적인 피해 영향범위를 판단한 것이다. 사고대비물질 중 액체상 물질인 질산, 메탄올, 아세트산에 대하여 독성 누출 시 피해 영향범위를 산정하였고, 저장 및 누출량에 따른 독성피해 영향범위를 판단할 수 있는 상관관계식을 도출하였다. 본 연구의 상관관계식으로 산정된 독성 누출시 피해 영향범위 결과와 실제 사업장의 사고 시나리오에 따른 KORA(장외영향평가서, 위해관리계획서 작성 지원 범용프로그램) 결과를 비교하여 적용 및 검증을 실시하였다. 따라서 본 연구의 물질별 상관관계식은 도로 혹은 사업장에서 사고대비물질 누출사고가 발생했을 경우, 독성피해 영향범위를 빠르게 판단함으로써 비상조치계획의 수립과 비상상황에 신속하게 대응할 수 있을 것이다. 또한, 영세 및 중소기업 사업장은 화학물질관리법에 따른 장외영향평가와 위해관리계획서를 제출할 때 위험성평가 활용이 가능하며, 저장 및 누출량에 따라 예상되는 독성피해 영향범위를 간단하게 확인 및 평가할 수 있을 것이다.

• 한국산학기술학회논문지
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• 제18권5호
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• pp.262-267
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• 2017

LNG 운반선용 구형 탱크의 제작을 위해서는 탱크의 크기에 따라 별도의 공장 설비가 필요하며 시설 투자의 한계로 인해 현실적으로 조선소에서 다양한 크기의 완전 구형 LNG 탱크를 제작하는 것은 매우 어려운 일이다. 다양한 용량의 LNG 탱크 제작을 위해서는 기존 구형 탱크의 중앙부에 원통 형태의 확장부를 삽입하여 적재 용량을 키우는 방법이 효과적이다. 본 연구에서는 원통 확장부를 갖는 구형 LNG 탱크에 대하여 수평 가속도에 의한 동적 압력분포 산출식을 유도하였다. 본 논문에서 유도한 압력 분포 산출식을 이용함으로써 원통 확장부를 갖는 구형 탱크를 화물창 형식으로 하는 LNG 운반선의 구조설계 시 구조 안전성 평가를 위한 동적 설계하중을 간편하게 구하여 해석에 적용할 수 있다. 또한, 이미 개발되어 있는 원통 확장부를 갖는 구형 LNG 탱크의 정적 하중에 대한 설계하중 산출식과 결합함으로써 정적 및 동적하중을 모두 고려한 정도 높은 간이해석법의 개발이 가능하며, 이를 통해 초기 견적 시 많은 시간과 비용을 소요하는 유한요소 해석을 대신하여 짧은 시간에 정도 높은 물량 산출이 가능할 것으로 기대된다.

• 감성과학
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• 제20권1호
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• pp.95-104
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• 2017

분노반응검사(Evans & Stangelang, 1971)는 분노를 유발하는 자극의 관점에서 분노수준을 평가하는 도구이다. 그러나 이는 고령자를 대상으로 사용하기에는 문항수가 너무 많아 적은 수의 문항으로 구성된 분노반응검사가 필요하다. 본 연구의 목적은 신뢰성이 높고 타당한 단축형 분노반응검사를 제작하는 것이다. 연구 1에서는 60세 이상의 고령자들에게 76문항으로 구성된 분노반응검사를 실시하였으며, 검사이론에 기초하여 76개의 문항들 중에서 10개의 문항을 추출하여 단축형 분노반응검사를 제작하였다. 연구 2에서는 60세 이상의 고령자들로 구성된 또 다른 표본을 대상으로 단축형 분노반응검사와 타당도 확인을 위한 검사들을 함께 실시하여 신뢰도와 타당도를 평가하였다. 노인용 단축형 분노반응검사의 Cronbach 는 .79로 양호한 수준의 신되도를 보였다. 노인용 단축형 분노반응검사는 특성분노를 반영하는 검사이므로, 특성분노를 측정하는 검사점수와 상관이 높아야하고, 분노의 다른 측면을 반영하는 점수와는 낮은 상관을 보여야 타당하다. 노인용 단축형 분노반응검사 점수는 상태-특성 표현 척도의 특성분노 점수와 .60이상의 높은 상관을 보였으며, 분노표출 점수와 .39의 상관을 보였고, 적대감 점수와 .41의 상관을 보였다. 결론적으로, 본 연구에서 제작한 단축형 분노반응검사는 신뢰할 수 있고 타당한 검사인 것으로 나타났다.

• Imaging Science in Dentistry
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• 제32권3호
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• pp.141-145
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• 2002

Purpose : The purpose of this study was to propose standard values for alveolar and basal bone in normal adult mandibles, and radiologically analyze the remodeling process of the edentulous mandible by examining molar areas and comparing them to the established normal values. Materials and Methods : Panoramic and CT scans of mandible were performed on 20 normal adults and 20 edentulous or partially edentulous adults. In both groups, arch half diameter and distance of alveolar bone were measured. Also the distance from the mandibular canal to the caudal edges, the buccal and lingual external borders of basal bone, were measured. A statistical comparison between the mean values of normal and edentulous mandibles was carried out in the selected areas. Results : There was evidence of decreasing arch half diameter and distance in the edentulous mandible, but statistically no significant change was seen between the normal and edentulous alveolar bone. There was evidence of decreasing buccal basal bone and increasing in the lingual basal bone in the edentulous mandible. A statistically significant difference between normal and edentulous mandibles was noted in the buccal basal bone. Conclusion: There was an inward and forward atrophic change of the edentulous mandibular molar area compared to the control. CT scanning required the use of sophisticated and expensive procedures to analyze the remodeling process of edentulous mandibles. Consequently, the development and application of a more simplified and objective radiographic procedure for broad and long-term study of remodeling procedures of edentulous mandible was recommended.

• Structural Engineering and Mechanics
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• 제32권3호
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• pp.383-398
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• 2009

Applying nonlinear statistical analysis methods in estimating the performance of structures in earthquakes is strongly considered these days. This is due to the methods' simplicity, timely lower cost and reliable estimation in seismic responses in comparison with time-history nonlinear dynamic analysis. Among nonlinear methods, simplified to be incorporated in the future guidelines, Modal Pushover Analysis, known by the abbreviated name of MPA, simply models nonlinear behavior of structures; and presents a very proper estimation of nonlinear dynamic analysis using lateral load pattern appropriate to the mass. Mostly, two kinds of connecting joints, 'hinge' and 'rigid', are carried out in different type of steel structures. However, it should be highly considered that nominal hinge joints usually experience some percentages of fixity and nominal rigid connections do not employ totally rigid. Therefore, concerning the importance of these structures and the significant flexibility effect of connections on force distribution and elements deformation, these connections can be considered as semi-rigid with various percentages of fixity. Since it seems, the application and implementation of MPA method has not been studied on moment-resistant steel frames with semi rigid connections, this research focuses on this topic and issue. In this regard several rigid and semi-rigid steel bending frames with different percentages of fixity are selected. The structural design is performed based on weak beam and strong column. Followed by that, the MPA method is used as an approximated method and Nonlinear Response History Analysis (NL-RHA) as the exact one. Studying the performance of semi-rigid frames in height shows that MPA technique offers reasonably reliable results in these frames. The methods accuracy seems to decrease, when the number of stories increases and does decrease in correlation with the semi-rigidity percentages. This generally implies that the method can be used as a proper device in seismic estimation of different types of low and mid-rise buildings with semi-rigid connections.